Prior art optical switches, such as that disclosed by Fouquet, et al. in U.S. Pat. No. 5,699,462, assigned to Agilent Technologies, operate by the principle of total internal reflection. Two arrays of parallel optical waveguides fabricated in the plane of a transparent dielectric sheet are arranged in a crossing pattern. This sheet is called the PLC. A vertical cavity or xe2x80x9ctrenchxe2x80x9d is formed at each cross point with a wall oriented such that when the cavity is empty of fluid, light travelling in one waveguide is transferred to the crossing waveguide by total internal reflection. When a cavity is filled with a fluid having an optical index matching that of the waveguide light passes directly across the trench, re-entering and continuing in the original waveguide without appreciable loss. By this means, light is switched between the continuing waveguide and a crossing waveguide by transferring fluid into or out of the associated trench.
As shown in FIG. 1, fluid transfer is accomplished by heating the fluid with an electrical resistor to generate a bubble within the trench. Heaters are fabricated in an array on a silicon substrate that is positioned parallel to and in alignment with the trench array, separated from it by a narrow gap. This substrate is referred to as the MCC. Hence, a heater is positioned opposite the mouth of each trench. Applying an electrical current to a heater causes nearby fluid to evaporate to form a vapor bubble that expands into the trench, displacing the fluid there and causing light to reflect between crossing channels.
The present optical switch operates in two stages. In the first stage, the bubble is xe2x80x9cblownxe2x80x9d into the trench. In the second stage, the sidewalls are heated to achieve a dry wall condition by an improved the thermal transfer path from the heat source to the reflecting wall. Separate side heaters are placed proximate to a direct thermal path to the sidewalls. This results in a switch that is more stable, energy efficient, and has a longer mean time to failure.
Generally, there are two types of heaters: central and side. The central heater applies heat to create a bubble. The side heaters apply heat through a direct thermal path to dry the sidewalls. In a first embodiment, the side heaters are in direct contact with the waveguide substrate. The side and central heaters may be constructed on separate substrates. In a second embodiment, the side heaters reside on the silicon substrate. The direct thermal path may be a separate thermal stud in contact with the silicon and waveguide substrates or a thermal stud integrated into the waveguide substrate.